Magnetic contouring system



April 29, 1952 w. M. POWELL 2,594,939

MAGNETIC CONTOURING SYSTEM Filed Sept. 10, 1948 2 SHEETS-SHEET 1 hg v "v $2 g w INVENTOR. ML 501v M POWELL A 7'7'ORNEK April 29, 1952 w. M. Pb ELL 2,594,989

MAGNETIC CONTOURING SYSTEM Filed Sept. 10, 1948 INVEVTOR. WILSON M. Powsu.

fla /4% ATTORNEY Patented Apr. 29, 1952 MAGNETIC GONTOURING SYSTEM Wilson M. Powell, Berkeley, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application September 10, 1948, Serial No. 48,747

16 Claims.

My invention relates to a magnetic graphing method and device and, in particular, to an arrangement for contouring the intensity of a magnetic field about the exposed face of a magnetic pole piece.

The primary, object of this invention is to provide a simple arrangement for contouring the in tensity of a magnetic field.

Another object of this inventionis to provide a method of marking on a paper overlay all points of an equal predetermined flux intensity of a magnetic pole.

A further object of this invention is to provide a simple, accurate, and economical method of plotting the magnetic field intensity of a magnetic field.

Other objects and advantages of my invention will be apparent from a further study of the following specification, claims, and drawings. For a better understanding of my invention, therefore, reference is made in the following description to the accompanying drawings, in which:

Figure 1 is an assembly view, partly diagrammatic and partly perspective illustrating a preferred embodiment of my invention;

Fig. 2 is a vertical sectional view of the search coil and supporting tube taken axially of the latter (Fig. '1);

Fig. 3 is a plan view of the collimating lens I9 shown in Fig. 1;

Fig. tie a sectional view of the collimating lens of Fig. 3 taken on line 4-4 of the latter;

Fig. 5 is a typical pattern obtained with my invention from a rectangular magnetic pole piece such as is shown in Fig. 6; and

Fig. 6 is a perspective view of an electroma net of which a flux density contour is desired.

Reference is now made to Fig. 1 diagrammatically showing my magnetic contouring system in which a preferably cylindrical search coil I is mounted on and frictionally supported by a vertical nonmagnetic support tube 2 threaded into an electrically insulating and nonmagnetic search base 3 which may be composed of an insulator such as polystyrene. be supported at any desired height on support tube 2 by means of a phosphor-bronze spring 59 (Fig. 2). silver soldered to the inside of a nonmagnetic coil base 45 so as to bear against the wall of support tube 2, thereby frictionally supporting the search coil. Coil I is preferably formed of about two thousand turns of number 42 wire wound on base 45 so as to give an effective coil area of approximately twenty thousand square centimeters. The search base 3 is sep- Search coil I may arat'ed from direct contact with the face of a 7' magnetic pole piece I to be probed through the utilization of a paper contour sheet 8 of relatively thin stock '(a satisfactory thickness having been found to be .002 inches in thickness) entirely covering such face. In series with and identical to the search coil I but connected in opposition thereto, is a stationary compensating coil 9 which is placed in the mensurable magnetic field to compensate for any overall change in magnetic flux density. In practice, the compensating coil 9 is placed in a convenient loca-.,,

tion on sheet 8 out of the way of the course of the search coil I. When probing of the area beneath the compensating coil 9 is desired the latter is then moved to a new location on the sheet. When the search base is moved through the torque tending to return to its neutral position a plane mirror I4 mounted on the suspension I 3. I have found that a DArsonval galvanometer with the restoring-torque spring removed or a galvanometer for which the restoring torque is compensated, such as in Patent No. 2,356,608 issued to Lorin OBryan, will operate satisfactorily. To one side of the galvanometer I9 is provided I a light beam source I5 containing a lamp [6, preferably of the point source type, a convex collimating lens I9, and a convex focusing lens 29. The convex collimating lens I9 (shown in Figs. 3 and 4) is covered on one side with a mask 2I in which there are two diametrically and. vertically aligned apertures 22 and 25; the first mentioned and upper aperture being circular and provided with a vertically centered cross-hair 29, and the lower aperture 25 being in the form of an elongated rectangle whose longer sides are symmetrically disposed with respect to the diameter including cross-hair 2B. Collimating lens I9 serves to collimate the light of lamp I6 into two vertically aligned beams having the shape of apertures 22 and 25; such beams then pass through convex lens 20 which focuses the beams upon galvanometer mirror I4.

Disposed to one side of the mirror I4 is an elongated scale 21 divided in millimeters and curved about the filament I3 as a center at a convenient radial distance therefrom. Slidably carried along a slot 29 disposed longitudinally and spaced from the bottom of scale 21 in the plane formed by the light source IS, the mirror 14, and the scale 2'! and thus being in the path or the lower portion of the beam reflected from mirror I4, is a photo-electric cell unit 23 which may be secured in an adjusted position along slot 29 by a support arm 38 attached to photocell 28 and a thumb-screw 3| adapted to fit slot 23. The degree of rotary motion or mirror i4 is indicative of the extent orany magnetic flux change, and the reflection of the upper beam of light source It from mirror M on scale 21 provices a direct measure of such change. Photoelectric cell unit 28 is provided with an opaque hood 24 having a single opening as rectangular aperture 32 identical with that of aperture 25 or collimating lens 19 for the admission of the lower rectangular beam of light reflected from mirror 14. Aperture 32 in photo-electric cell 23 is identical with aperture 23 in order that photoelectic cell 28 will be activated only when the iellected lower beam falls directly into aperture 32, a deviation of only one millimeter of the lower rectangular beam from aperture 32 being sufiiclent to prevent energization of photo-electric cell 28.

A voltage generated by the light sensitive surface or hoto-electric cell 28 when the lower rectangular beam reflected from mirrdr l4 penetrates the rectangular orifice 32 and actives the photo-sensitive surface of ce-l 2B is applied to a voltage amplifier 33 disposed near the photoelectric cell 28 through conductors 35. Voltage amplifier 33 is of the direct-coupled type for direct current amplification, and satisfactory operation may be obtained with the directcoupled amplifier shown in Fig. 15c, page 376, of the Radio Engineers Handbook by Frederick Emmons Terman, 1943 edition. The output of amplifier 33 operates a relay (of which only the contacts 34 are shown) for closing the primary circuit 31 of an adjacent transformer 38. The ratio of transformation of transformer 38 is about 100 to l in order that the primary power line voltage of 115 voltsA. C. will be converted in a secondary winding 39, one end of which is grounded, to at least 10,000 volts. Satisfactory operation has also been obtained by using a stepdown transformer for reducing the power line voltage to approximately six volts and applying this low voltage to the primary of a Ford spark coil, the output of which is also about 10,000 volts.

The output of the transformer secondary winding 39 is led, by means of an insulated high voltage cable 40, into the search base 3. The cable 40 enters base 3 through the center of one of the sides and parallel to the bottom of the base, then turns downward to a 90-degree angle directly under the support tube 2, terminating and barely breaking through the bottom surface of the base at a point 43. Cable 40 is stripped of insulation for approximately one-half inch back of point 43 in order that no insulation will interfere with the exposure of the bare wire at point 43. Photoelectric cell amplifier 33 operates to energize the relay associated with contacts 34 and thereby permits power to be applied to the primary 3'! of transformer 38. The high voltage induced in the secondary winding 39 and transmitted along cable 40 to point 43 is sufficient to permit a spark to arc from point 43 to the grounded magnetic pole piece 1 puncturing a small hole in the paper contour sheet 8.

In operating my magnetic contouring system, a control handle 46 articularly attached to the base assembly 3 by a hinge 49 is used to horizontally sweep the search coil l across the magnetic flux field which is perpendicular to the surface of magnet pole piece I. As the search coil I passes through variations in fiux intensity. a varying voltage is induced in search coil l which is applied to galvanometer I0. The flux changes encountered by search coil l are integrated by galvanometer l0 and appear as incremental voltage increases whenever coil l passes through magnetic flux of increasing intensity and incremental decreases whenever coil 1 passes through fiux of decreasing intensity. The varying voltage applied to galvanometer l0 efiects a rotary motion of mirror l4 causing the beam of light of lamp 16 to traverse scale 21 in accordance with the flux variations. Photo-electric cell 23 is adjusted along scale 2! at a preselected position corresponding to a desired flux intensity and is, therefore, activated whenever the lower beam of light formed by aperture 25 falls on aperture 32. Thus, whenever a preselected magnetic flux in tensity is encountered by search coil l during the traverse of the pole piece 1, mirror 14 of galvanometer l0 reflects a beam of light onto photoelectric cell 28 generating a voltage in the photocell which is transmitted to voltage amplifier 33. The contacts 34 associated with amplifier 33 remain closed during the generation of the photocell voltage permitting transformer 38 to be energized and an arc to be formed between point 43 and pole piece I through paper sheet 8. A series of small holes is punctured in paper sheet 8 when ever search coil I is probed into an area of preselected fiux intensity. By altering the position of photo-cell 28 along scale 21, the system will respond to some other value of flux density. The small punctures in contour sheet 8 corresponding to each particular scale setting are connected to give a series of lines of constant vertical magnetic field intensity. Since the flux value of each contour line is known, it is merely a matter of simple interpolation to determine the flux at any point between successive contour lines. If desired, search coil I may be moved vertically along support rod 2 so as to permit comparisons to be made of the distribution of the magnetic field at different distances from the face of the magnetic pole piece.

Fig. 5 illustrates magnetic contour lines 50 of a typical flux pattern on the contour sheet 8 as might be derived from a flux field probe with my contouring system on pole face I of an electromagnet 5! having a closed external core 52 and separate pole windings 55 (Fig. 6). The lines 50 are spaced widely apart near the center of contour sheet 8 where the flux is relatively uni form and closely spaced near the edges where the leakage flux effects relatively abrupt changes in perimetrical flux density. By means of adequate magnetic shimming, then subsequent replotting of the flux density contour lines, any desired flux density pattern may be obtained.

While I have described the salient features of this invention with respect to one embodiment, it will, of course, be apparent that numerous modifications may be made within the spirit and scope ing action would be as described herein. I do not, therefore, desire to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

What is claimed is:

1. A method of contouring the flux intensity emanating from a magnetic surface which comprises ascertaining continuously the flux intensity at contiguous points in a plane spaced from said surface and simultaneously perforating a thin record surface disposed between said plane and said magnetic surface in accordance with such points of equal fiux density as are encountered.

2. A method of contouring the flux intensity emanating from a magnetic surface which comprises ascertaining the flux intensity of said magnetic surface at contiguous points in a plane spaced from said surface and simultaneously causing an electric arc to pierce a thin record surface placed on said magnetic surface whenever the magnetic flux reaches some predetermined value.

3. A vectorial field testing device comprising a probe, 2. field intensity detector carried by said probe, a marking device adapted to record data upon a recording sheet disposed in said vectorial field, and means controlled by said field intensity detector for operating said device whenever the strength of the field attains a predetermined value.

4. A magnetic field testing device comprising a probe, a field intensity detector and a marking device adapted to record data upon a recording sheet disposed in said magnetic field, said device being carried by said probe, and means controlled by said field intensity detector for operating said device whenever the strength of the field attains a predetermined value.

5. An apparatus for plotting the contour of a magnetic field comprising an element responsive to the flux density of said magnetic field, means whereby said magnetic-responsive element may be moved through said magnetic field, a recording element adapted to be moved along a path within said magnetic field corresponding to the path traversed by said magnetic-responsive element, and means responsive to said magnetic-responsive element for actuating said recording element.

6. A magnetic field testing device comprising a probe adapted to be moved over a recording sheet disposed on the inhomogeneous magnetic surface of a magnet, a search coil carried by said probe, a flux integrating meter associated with said search coil, a circuit terminal carried by said probe adjacent said recording sheet, means controlled by the net change in magnetic flux through said flux integrating meter as said probe is progressively moved back and forth across said recording sheet for producing a spark at said terminal each time the net change in magnetic flux attains a predetermined value, whereby a series of marks is made on said recording sheet along lines indicative of the magnetic flux distribution.

6 'I. In combination with a. magnet pole face having a non-uniform magnetic field there: through, a testing apparatus receiving impulses from said magnetic field and imposing said im-.- pulses upon a galvanometer including a mirror,

a light source including a light-transmitting aperture, a photo-sensitive element having a relay associated therewith, a high voltage sparkproducing means operated by said relay and means including said mirror for. focusing the image of said aperture on said photo-sensitive element at a predetermined mirror, position whereby said relay actuates said spark-producing means.

8. Means for plotting magnetic field intensities and comprising in combination, a magnet pole face, means establishing a non-uniform magnetic field therethrough, a surface upon which the relative intensities of said field are to be plotted, means for applying a mark upon said surface corresponding in location and field intensity value to that position within the field and that relative field intensity at which a reading is simultaneously being taken, a probe adapted to be moved through said field, galvanometer means connected to said probe and adapted to be moved to a position corresponding to the relative field intensity encountered by said probe, and an adjustably calibrated control means for actuating said marking means, said control means being actuated only when the position assumed by said galvanometer means corresponds to the calibrated position of said control means.

9. Apparatus as defined in claim 8 wherein said surface includes a recording sheet disposed on the magnet pole face.

10. Apparatus as defined in claim 8 wherein said means for applying a mark includes a sparkproducing means.

11. Apparatus as defined in claim 8 wherein said control means includes a photo-sensitive element actuated by light reflected from a mirror carried by said galvanometer.

12. A method of contouring the flux intensity at various levels above a magnetic surface which comprises ascertaining the flux intensity at contiguous points in a plane spaced from said surface and simultaneously spark-perforating a thin record surface directly beneath said points whenever the magnetic flux reaches some predetermined value, and repeating the said ascertaining and recording steps in planes variously spaced from said surface to provide a depthvarying magnetic contouring record of the field emanating from said magnetic surface.

13. A magnetic field testing device comprising an element responsive to the flux density of said magnetic field, means movable across said magnetic field and serving also to support said element at adjustable positions in the direction of said field, a recording element carried by said means, and means responsive to said element for actuating said recording element.

14. Apparatus as defined in claim 13 including a second element responsive to the flux density of said magnetic field and connected in series opposition to saidfirst element to compensate for overall changes in magnetic fiux density.

15. A magnetic field testing device comprising a search coil, means movable across said magnetic field and serving to support said element in general axial coincidence with the direction of said field, a recording element carried by said supporting means and disposed on the axis of said search coil and means responsive to said element for actuating said recording element.

16. Apparatus as defined in claim 15 wherein said recording element comprises a spark producing means, and a spark-perforable recording sheet disposed in a plane extending generally normal to the direction of said field.

- WILSON M. POWELL.

REFERENCES CITED The following references are of record in the iile of this patent:

Number UNITED STATES PATENTS Name Date Stoekle et a1. Aug. 13, 1940 Schweitzer Sept. 8, 1915 Dixon Sept. 23, 1919 Drake Oct. 23, 1934 Bucky Dec. 25, 1934 Billstein May 12, 1942 Swift, June 13, 1944 Iams Apr. 18, 1950 

